gpio: use class_groups instead of class_attrs

The class_attrs pointer is long depreciated, and is about to be finally
removed, so move to use the class_groups pointer instead.
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: <linux-gpio@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib-sysfs.c

@@ -479,6 +479,7 @@ static ssize_t export_store(struct class *class,
 		pr_debug("%s: status %d\n", __func__, status);
 	return status ? : len;
 }
+static CLASS_ATTR_WO(export);
 
 static ssize_t unexport_store(struct class *class,
 				struct class_attribute *attr,
@@ -514,18 +515,20 @@ static ssize_t unexport_store(struct class *class,
 		pr_debug("%s: status %d\n", __func__, status);
 	return status ? : len;
 }
+static CLASS_ATTR_WO(unexport);
 
-static struct class_attribute gpio_class_attrs[] = {
-	__ATTR(export, 0200, NULL, export_store),
-	__ATTR(unexport, 0200, NULL, unexport_store),
-	__ATTR_NULL,
+static struct attribute *gpio_class_attrs[] = {
+	&class_attr_export.attr,
+	&class_attr_unexport.attr,
+	NULL,
 };
+ATTRIBUTE_GROUPS(gpio_class);
 
 static struct class gpio_class = {
 	.name =		"gpio",
 	.owner =	THIS_MODULE,
 
-	.class_attrs =	gpio_class_attrs,
+	.class_groups = gpio_class_groups,
 };